An apparatus for generating orthogonally polarized terahertz waves

Abstract

The application aims to provide a device for generating orthogonal polarization terahertz waves, comprising a pump source, an AFB-KTP crystal, a PIGaP crystal, a first resonant cavity mirror, a second resonant cavity mirror and a parabolic mirror; two terahertz waves with equal frequencies and orthogonal polarization directions can be generated simultaneously, and the terahertz wave conversion efficiency is improved. By setting the reverse period of the AFB-KTP crystal, the wavelengths of the two o light and the two e light can be changed, and the frequency of the output terahertz wave is changed. By setting the period polarization distribution of the PIGaP crystal, the Stokes cascade difference frequency can be selectively enhanced, and the anti-Stokes cascade difference frequency can be suppressed, and the overall terahertz wave optical conversion efficiency is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of terahertz wave application, and particularly relates to a device for generating orthogonal polarization terahertz waves. BACKGROUND

[0002] Terahertz (THz) is electromagnetic wave with frequency in the range of 0.1-10 THz (1 THz = 10 12 Hz), which is located between millimeter wave and infrared in the electromagnetic spectrum, and is the transition region from macroscopic theory to microscopic theory. Due to the special location, THz wave has great scientific research value and broad application prospect in the fields of basic research such as physics, chemistry, astronomy, molecular spectroscopy, life science and medical science, and application research such as medical imaging, environmental monitoring, material detection, food detection, radio astronomy, mobile communication, satellite communication and military radar. THz wave is mainly applied in the following fields:

[0003] (1) Imaging field

[0004] THz wave imaging is different from ordinary optical image or X-ray image, each pixel in the pulse THz wave image contains the entire THz waveform, not just the intensity of the light beam. The Fourier transform of the THz waveform can also extract the spectral information of the pixel. Therefore, THz wave imaging not only identifies the target through its contour, but also obtains the complex information of the target.

[0005] (2) Biomedical technology field

[0006] Due to the "fingerprint" characteristics of THz band, the interaction with medium contains rich physical and chemical information, and the low energy ensures that it can be applied to the field of biomedical imaging. Since the THz light source is composed of different complex polarized light waves, different polarized light can be used to collect information of the medium to obtain more accurate diagnostic information of pathological tissues, so THz wave has a significant role in clinical diagnosis and treatment of cancer.

[0007] (3) Nondestructive testing field

[0008] The penetration of THz wave can be well applied to the fields of nondestructive testing and THz imaging. By using THz time-domain spectroscopy technology, non-contact and non-destructive conditions can be realized, and non-polar dielectric materials such as clothes, cartons and plastics can be penetrated, so that the chemical properties of the medium can be detected, new biological characteristic information and identification basis of grain storage pests in the THz band can be provided, and a new method of identification and research complementary to other detection technologies can be established, so that the grain storage pests and their types can be detected quickly and conveniently, which has important practical significance for investigation and monitoring of grain storage pests, and acceleration of rapid detection and quarantine of pests at ports and accurate detection of grain storage pests in grain stores.

[0009] (4) Communication field

[0010] THz wave has wide bandwidth, good directivity and high transmission rate, so it has great potential in space high-speed communication and radar application, and has the application prospect of military and civilian combination and balanced and coordinated development. Since THz wave is sensitive to water molecules, it can realize secret communication in the atmosphere. Compared with visible light and infrared, THz wave has better directivity due to long wavelength, so it can realize space communication with extremely high bandwidth in clouds and fog.

[0011] (5) National security field

[0012] THz wave has good directivity and narrow beam, and has strong cloud and smoke penetration ability. In military application, THz wave is used for correction of missile terminal precise guidance to improve guidance accuracy, which has high military application value.

[0013] The main problem at present is that there is a lack of a THz source capable of generating high-power, high-quality and high-efficiency THz wave, and low cost and operating at room temperature. SUMMARY

[0014] The purpose of the present application is to provide a device for generating orthogonal polarization THz wave, which can generate two THz waves with equal frequency and orthogonal polarization direction at the same time, and improve the conversion efficiency of THz wave.

[0015] The purpose of the present application is achieved in the following manner: a device for generating orthogonal polarization THz wave, comprising a pump source, an AFB-KTP crystal, a PIGaP crystal, a first resonant cavity mirror, a second resonant cavity mirror and a parabolic mirror.

[0016] The pump light emitted from the pump source is incident into the AFB-KTP crystal through the first resonant cavity mirror to generate first mixed light; the first mixed light contains pump light, two signal lights λ1 and λ2, and two idler lights λ3 and λ4; the first mixed light is incident into the PIGaP crystal, and λ1 and λ2 generate a first group of cascade light and a first THz wave through cascade optical difference frequency effect in the PIGaP crystal, and λ3 and λ4 generate a second group of cascade light and a second THz wave through cascade optical difference frequency effect in the PIGaP crystal; the first THz wave and the second THz wave are combined into one THz wave; the above two groups of cascade light and the THz wave are mixed with the pump light to form second mixed light; the THz wave in the second mixed light is reflected by the parabolic mirror, and the two groups of cascade light in the second mixed light and the pump light form third mixed light, which is incident into the second resonant cavity mirror through the parabolic mirror; the first group of cascade light oscillates back and forth in the resonant cavity composed of the first resonant cavity mirror and the second resonant cavity mirror, and the fourth mixed light composed of the second group of cascade light and the pump light passes through the second resonant cavity mirror.

[0017] The polarization directions of λ1 and λ2 are the same, the polarization directions of λ3 and λ4 are the same, and the polarization directions of λ1 and λ3 are perpendicular; the frequencies of the terahertz waves generated by λ1 and λ2 in the PIGaP crystal through the cascaded optical difference frequency effect are the same as the frequencies of the terahertz waves generated by λ3 and λ4 in the PIGaP crystal through the cascaded optical difference frequency effect;

[0018] The plane of the light beam propagation is the plane determined by the X-axis and the Y-axis, and the Z-axis is perpendicular to the plane of the light beam propagation; the initial propagation direction of the pump light emitted from the pump source is the positive direction of the X-axis, and the propagation direction of the terahertz wave reflected by the parabolic mirror is the positive direction of the Y-axis; the propagation directions of the first, second, third and fourth mixed lights are the positive direction of the X-axis.

[0019] The polarization direction of the pump light is the Y-axis, the polarization directions of λ1 and λ2 are the Z-axis, and the polarization directions of λ3 and λ4 are the Y-axis; the polarization direction of the first group of cascaded light is the Z-axis, and the polarization direction of the second group of cascaded light is the Y-axis; the polarization direction of the first terahertz wave is the Z-axis, and the polarization direction of the second terahertz wave is the Y-axis, and the terahertz wave is a beam of orthogonally polarized terahertz waves.

[0020] The first resonant cavity mirror and the second resonant cavity mirror are both concave mirrors; the first resonant cavity mirror and the second resonant cavity mirror are highly transmissive to the pump light and highly reflective to the first group of cascaded light, the first resonant cavity mirror is highly reflective to the second group of cascaded light, and the second resonant cavity mirror is highly transmissive to the second group of cascaded light.

[0021] The transmittance of the first resonant cavity mirror to the pump light is 99.9%, the reflectance of the first resonant cavity mirror to the first group of cascaded light is 99.9%, and the reflectance of the first resonant cavity mirror to the second group of cascaded light is 99.9%; the reflectance of the second resonant cavity mirror to the first group of cascaded light is 95%, and the transmittance of the second resonant cavity mirror to the second group of cascaded light and the pump light is 99.9%.

[0022] The AFB-KTP crystal and the PIGaP crystal are both cuboids, and are rectangular in the X-Y plane; the AFB-KTP crystal is a KTP crystal without adhesive bonding; and the PIGaP crystal is a periodically inverted GaP crystal.

[0023] The inversion period of the AFB-KTP crystal is 12157 μm, the wavelengths of the signal light λ1 and λ2 are 1.0407 μm and 1.0389 μm respectively, and the wavelengths of the idler light λ3 and λ4 are 1.0903 μm and 1.0884 μm respectively; and the inversion period of the PIGaP crystal is 271 μm.

[0024] A small hole only allowing the third mixed light to pass through is provided at the center of the parabolic mirror.

[0025] The frequency difference of adjacent cascade lights in the first group of cascade lights and the second group of cascade lights is equal to the frequency size of the terahertz wave.

[0026] Compared with the prior art, the device for generating orthogonal polarization terahertz wave has the following advantages:

[0027] (1) By setting the inversion period of the AFB-KTP crystal, the wavelength of the two o lights and the two e lights output can be changed, and the frequency of the output terahertz wave can be changed.

[0028] (2) By setting the period polarization distribution of the PIGaP crystal, the Stokes cascade difference frequency can be selectively enhanced, the anti-Stokes cascade difference frequency can be suppressed, and the overall terahertz wave optical conversion efficiency can be improved. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 is the structural principle diagram of the application.

[0030] Figure 2 is the relationship between the different inversion periods of the AFB-KTP crystal and the wavelengths of the two o lights (i.e. idler light 1 and idler light 2) and the two e lights (i.e. signal light 1 and signal light 2) generated.

[0031] Figure 3 is a graph of the intensity of the first terahertz wave changing with the length of the PIGaP crystal.

[0032] Figure 4 is a graph of the intensity of the second terahertz wave changing with the length of the PIGaP crystal. DETAILED DESCRIPTION

[0033] The technical solutions of the application will be described clearly and completely in combination with the drawings and specific embodiments. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the application, and cannot be understood as a limitation on the protection scope of the application. Skilled persons in the art can make some non-essential improvements and adjustments according to the content of the application. In the application, unless otherwise explicitly specified and limited, the technical terms used in the application should be understood as the general meaning understood by the skilled person in the art.

[0034] As shown in the accompanying Figure 1 A device for generating orthogonal polarization terahertz wave, characterized by comprising a pump source 1, an AFB-KTP crystal 4, a PIGaP crystal 6, a first resonant cavity mirror 3, a second resonant cavity mirror 11, and a parabolic mirror 8.

[0035] The pump light 2 emitted from the pump source 1 is incident into the AFB-KTP crystal 4 through the first resonant cavity mirror 3, and the first mixed light 5 is generated. The first mixed light 5 includes the pump light 2, two signal lights λ1 (signal light 1) and λ2 (signal light 2), and two idler lights λ3 (idler light 1) and λ4 (idler light 2). The first mixed light 5 is incident into the PIGaP crystal 6, and the λ1 and λ2 generate a first group of cascade lights and a first terahertz wave through the cascade optical difference frequency effect in the PIGaP crystal 6, and the λ3 and λ4 generate a second group of cascade lights and a second terahertz wave through the cascade optical difference frequency effect in the PIGaP crystal 6. The first terahertz wave and the second terahertz wave are combined into a terahertz wave 9. The above two groups of cascade lights, the terahertz wave 9 and the pump light 2 are mixed into the second mixed light 7. The terahertz wave 9 in the second mixed light 7 is reflected out through the parabolic mirror 8, and the two groups of cascade lights in the second mixed light 7 and the pump light 2 form the third mixed light 10, which passes through the parabolic mirror 8 and is incident into the second resonant cavity mirror 11. The first group of cascade lights oscillate back and forth in the resonant cavity composed of the first resonant cavity mirror 3 and the second resonant cavity mirror 11, and the fourth mixed light 12 composed of the second group of cascade lights and the pump light 2 passes through the second resonant cavity mirror 11.

[0036] The wavelengths of the λ1, λ2, λ3 and λ4 depend on the size of the inversion period of the AFB-KTP crystal (4); by setting the inversion period of the AFB-KTP crystal (4), the terahertz waves generated by the λ1 and λ2 through the cascade optical difference frequency effect in the PIGaP crystal (6) have the same frequency as the terahertz waves generated by the λ3 and λ4 through the cascade optical difference frequency effect in the PIGaP crystal (6); specifically, as follows:

[0037] In the embodiment, the pump source 1 is a pulsed green laser, the wavelength of the pump light 2 is 532 nm, the pump power density is 1000 MW / cm 2 , the pulse width of the pump light is 10 ns, the repetition frequency is 10 Hz, and the beam diameter is 1 mm. The pump light 2 generates two e lights λ1 and λ2 and two o lights λ3 and λ4 through the reaction of the AFB-KTP crystal 4. The wavelengths of the two e lights λ1 and λ2 and the two o lights λ3 and λ4 depend on the size of the inversion period of the AFB-KTP crystal 4. The inversion period of the AFB-KTP crystal 4 is 12157 μm, as Figure 2As shown, λ1 and λ2 are signal light 1 and signal light 2 respectively, and the wavelengths are 1.0407 μm and 1.0389 μm respectively, λ3 and λ4 are idler light 1 and idler light 2 respectively, and the wavelengths are 1.0903 μm and 1.0884 μm respectively. By setting the inversion period of the PIGaP crystal 6 as 271 μm, the frequency of the terahertz wave 9 generated by the cascaded optical difference frequency effect of λ1 and λ2 in the PIGaP crystal 6 is the same as the frequency of the terahertz wave generated by the cascaded optical difference frequency effect of λ3 and λ4 in the PIGaP crystal 6. The frequency of the generated terahertz wave 9 is the frequency difference of the two beams of signal light 1 and signal light 2 or the two beams of idler light 1 and idler light 2, that is, 0.5 THz.

[0038] In the embodiment, the plane of the light beam propagation is the plane determined by the X axis and the Y axis, and the Z axis is perpendicular to the plane of the light beam propagation. The initial propagation direction of the pump light 2 emitted from the pump source 1 is the positive direction of the X axis, and the propagation direction of the terahertz wave 9 reflected by the parabolic mirror 8 is the positive direction of the Y axis. The propagation directions of the first mixed light 5, the second mixed light 7, the third mixed light 10 and the fourth mixed light 12 are the positive direction of the X axis.

[0039] In the embodiment, the polarization direction of the pump light 2 is the Y axis, the polarization direction of λ1 and λ2 is the Z axis, and the polarization direction of λ3 and λ4 is the Y axis. The polarization direction of the first group of cascaded light is the Z axis, and the polarization direction of the second group of cascaded light is the Y axis. The polarization direction of the first terahertz wave is the Z axis, the polarization direction of the second terahertz wave is the Y axis, and the terahertz wave 9 is a beam of orthogonally polarized terahertz waves.

[0040] In the embodiment, the first resonant cavity mirror 3, the parabolic mirror 8 and the second resonant cavity mirror 11 are all concave mirrors. The transmittance of the first resonant cavity mirror 3 to the pump light 2 is 99.9%, the reflectance of the first resonant cavity mirror 3 to the first group of cascaded light is 99.9%, and the reflectance of the first resonant cavity mirror 3 to the second group of cascaded light is 99.9%. The reflectance of the second resonant cavity mirror 11 to the first group of cascaded light is 95%, and the transmittance of the second resonant cavity mirror 11 to the second group of cascaded light and the pump light 2 is 99.9%.

[0041] The AFB-KTP crystal 4 is a binder-free KTP crystal. The PIGaP crystal 6 is a periodically inverted GaP crystal.

[0042] In the embodiment, the AFB-KTP crystal 4 and the PIGaP crystal 6 are cuboids, and are rectangular in the X-Y plane. The AFB-KTP crystal 4 is a binderless KTP crystal, and the size of the AFB-KTP crystal 4 is X×Y×Z=36.47 mm×4 mm×2 mm, and the length direction of the crystal is consistent with the positive direction of the X axis. The PIGaP crystal 6 is a periodically inverted GaP crystal, and by setting the inversion period thereof, the intensity of the generated terahertz wave 9 can be changed. The size of the PIGaP crystal 6 is X×Y×Z=30 mm×4 mm×2 mm, and the length direction of the crystal is consistent with the positive direction of the X axis, and the inversion period of the PIGaP crystal 6 is set to 271 μm, and the intensity of the first terahertz wave in the intensity of the generated terahertz wave 9 changes as shown in FIG. 5, and the intensity of the second terahertz wave changes as shown in FIG. 6. Figure 3 Figure 4

[0043] In the embodiment, a small hole only allowing the third mixed light 10 to pass through is arranged at the center of the parabolic mirror 8, and the diameter of the small hole is 1 mm.

[0044] The frequency difference between adjacent cascade lights in the first group of cascade lights and the second group of cascade lights is the frequency of the terahertz wave 9, that is, 0.5 THz.

[0045] The above-described embodiments are only examples and illustrations of the technical solutions of the present application, and are intended to facilitate understanding of the technical solutions of the present application by those skilled in the art, and the protection scope of the present application is not limited thereto. Each technical feature of the above-described embodiments can be combined arbitrarily, and in order to make the description brief, not all possible combinations of the technical features in the above-described embodiments are described, however, as long as the combinations of the technical features do not contradict each other or cannot be implemented, it should be considered that the combinations of the technical features are within the scope of the present application. The basic idea of the present application is the above-described basic scheme, and for those skilled in the art and any person skilled in the art, according to the teachings of the present application, various modified models, formulas, and parameters can be designed without requiring creative labor. Changes, modifications, replacements, equivalent replacements, and variations of the embodiments without departing from the principles and spirits of the present application should be considered as the protection scope of the present application.​​

Claims

1. A device for generating orthogonally polarized terahertz waves, characterized in that: Includes a pump source (1), an AFB-KTP crystal (4), a PIGaP crystal (6), a first resonant cavity mirror (3), a second resonant cavity mirror (11), and a parabolic mirror (8). Pump light (2) emitted from pump source (1) is incident into AFB-KTP crystal (4) through first resonant cavity mirror (3), generating first mixed light (5); the first mixed light (5) includes pump light (2), two signal lights λ1 and λ2, and two idler lights λ3 and λ4; the first mixed light (5) is incident into PIGaP crystal (6), λ1 and λ2 generate a first set of cascaded light and a first terahertz wave in PIGaP crystal (6) through cascaded optical difference frequency effect, λ3 and λ4 generate a second set of cascaded light and a second terahertz wave in PIGaP crystal (6) through cascaded optical difference frequency effect; the first terahertz wave and the second terahertz wave are combined into A beam of terahertz wave (9); the above two sets of cascaded light, the terahertz wave (9) and the pump light (2) are mixed to form the second mixing light (7); the terahertz wave (9) in the second mixing light (7) is reflected out by the parabolic mirror (8), the two sets of cascaded light in the second mixing light (7) and the pump light (2) form the third mixing light (10), the third mixing light (10) passes through the parabolic mirror (8) and is incident on the second resonant cavity mirror (11); the first set of cascaded light oscillates back and forth in the resonant cavity composed of the first resonant cavity mirror (3) and the second resonant cavity mirror (11), the fourth mixing light (12) composed of the second set of cascaded light and the pump light (2) passes through the second resonant cavity mirror (11). The polarization directions of λ1 and λ2 are the same, the polarization directions of λ3 and λ4 are the same, and the polarization directions of λ1 and λ3 are perpendicular; the terahertz waves generated by λ1 and λ2 in the PIGaP crystal (6) through the cascaded optical difference frequency effect have the same frequency as the terahertz waves generated by λ3 and λ4 in the PIGaP crystal (6) through the cascaded optical difference frequency effect. The plane in which the beam propagates is the plane defined by the X-axis and Y-axis, and the Z-axis is perpendicular to the plane in which the beam propagates; the initial propagation direction of the pump light (2) emitted from the pump source (1) is the positive X-axis, and the propagation direction of the terahertz wave (9) reflected by the parabolic mirror (8) is the positive Y-axis; the propagation directions of the first mixing light (5), the second mixing light (7), the third mixing light (10), and the fourth mixing light (12) are the positive X-axis.

2. The apparatus for generating orthogonally polarized terahertz waves according to claim 1, characterized in that: The polarization direction of the pump light (2) is the Y-axis, the polarization direction of λ1 and λ2 is the Z-axis, and the polarization direction of λ3 and λ4 is the Y-axis; the polarization direction of the first cascade light is the Z-axis, and the polarization direction of the second cascade light is the Y-axis; the polarization direction of the first terahertz wave is the Z-axis, the polarization direction of the second terahertz wave is the Y-axis, and the terahertz wave (9) is a beam of orthogonally polarized terahertz waves.

3. The apparatus for generating orthogonally polarized terahertz waves according to claim 1, characterized in that: Both the first resonant cavity mirror (3) and the second resonant cavity mirror (11) are concave mirrors; the first resonant cavity mirror (3) and the second resonant cavity mirror (11) have high transmission to the pump light (2) and high reflection to the first group of cascaded light, the first resonant cavity mirror (3) has high reflection to the second group of cascaded light, and the second resonant cavity mirror (11) has high transmission to the second group of cascaded light.

4. The apparatus for generating orthogonally polarized terahertz waves according to claim 3, characterized in that: The first resonant cavity mirror (3) has a transmittance of 99.9% for the pump light (2), a reflectance of 99.9% for the first set of cascaded light, and a reflectance of 99.9% for the second set of cascaded light; the second resonant cavity mirror (11) has a reflectance of 95% for the first set of cascaded light and a transmittance of 99.9% for the second set of cascaded light and the pump light (2).

5. The apparatus for generating orthogonally polarized terahertz waves according to claim 1, characterized in that: Both the AFB-KTP crystal (4) and the PIGaP crystal (6) are cuboids and are rectangular in the XY plane; the AFB-KTP crystal (4) is a KTP crystal without binder; the PIGaP crystal (6) is a periodically reversed GaP crystal.

6. The device for generating orthogonally polarized terahertz waves according to claim 1, characterized in that: The AFB-KTP crystal (4) has a reversal period of 12157 μm, and the wavelengths of the signal light λ1 and λ2 are 1.0407 μm and 1.0389 μm, respectively. The wavelengths of the idler light λ3 and λ4 are 1.0903 μm and 1.0884 μm, respectively. The PIGaP crystal (6) has a reversal period of 271 μm.

7. The apparatus for generating orthogonally polarized terahertz waves according to claim 1, characterized in that: A small hole is opened in the center of the parabolic mirror (8) that allows only the third mixing light (10) to pass through.

8. The apparatus for generating orthogonally polarized terahertz waves according to claim 1, characterized in that: The frequency difference between adjacent cascaded lights in the first and second cascaded lights is equal to the frequency of the terahertz wave (9).

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